This invention relates to cryocoolers, and to cryoprobes for use in cryosurgery.
Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue, causing the tissue to die, after which it will be absorbed by the body or expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases.
The use of cryosurgical probes for cryoablation of the prostate is described in Onik, Ultrasound-Guided Cryosurgery. Scientific American at 62 (January 1996) and Onik, Cohen, et al., Transrectal Ultrasound-Guided Percutaneous Radial Cryosurgical Ablation Of The Prostate, 72 Cancer 1291 (1993). In this procedure, generally referred to as cryoablation of the prostate, several cryosurgical probes are inserted through the skin in the perineal area (between the scrotum and the anus) which provides the easiest access to the prostate. The probes are pushed into the prostate gland through previously placed cannulas. Placement of the probes within the prostate gland is visualized with an ultrasound imaging probe placed in the rectum. The probes are quickly cooled to temperatures typically below xe2x88x92120 C. The prostate tissue is killed by the freezing, and any tumor or cancer within the prostate is also killed. The body will absorb some of the dead tissue over a period of several weeks. Other necrosed tissue may slough off through the urethra. The urethra, bladder neck sphincter and external sphincter are protected from freezing by a warming catheter placed in the urethra and continuously flushed with warm saline to keep the urethra from freezing.
Rapid re-warming of cryosurgical probes is desired. Cryosurgical probes are warmed to promote rapid thawing of the prostate, and upon thawing the prostate is frozen once again in a second cooling cycle. The probes cannot be removed from frozen tissue because the frozen tissue adheres to the probe. Forcible removal of a probe which is frozen to surrounding body tissue leads to extensive trauma. Thus many cryosurgical probes provide mechanisms for warming the cryosurgical probe with gas flow, condensation, electrical heating, etc.
A variety of cryosurgical instruments, variously referred to as cryoprobes, cryosurgical ablation devices, and cryostats and cryocoolers, have been available for cryosurgery. The preferred device uses Joule-Thomson cooling in devices known as Joule-Thomson cryostats. These devices take advantage of the fact that most gases, when rapidly expanded, become extremely cold. In these devices, a high pressure gas such as argon or nitrogen is expanded through a nozzle inside a small cylindrical sheath made of steel, and the Joule-Thomson expansion cools the steel sheath to sub-freezing cryogenic temperature very rapidly.
An exemplary device is illustrated in Sollami, Cryogenic Surgical Instrument, U.S. Pat. No. 3,800,552 (Apr. 2, 1974). Sollami shows a basic Joule-Thomson probe with a sheath made of metal, a fin-tube helical gas supply line leading into a Joule-Thomson nozzle which directs expanding gas into the probe. Expanded gas is exhausted over the fin-tube helical gas supply line, and pre-cools incoming high pressure gas. For this reason, the coiled supply line is referred to as a heat exchanger, and is beneficial because, by precooling incoming gas, it allows the probe to obtain lower temperatures.
Ben-Zion, Fast Changing Heating and Cooling Device and Method, U.S. Pat. No. 5,522,870 (Jun. 4, 1996) applies the general concepts of Joule-Thomson devices to a device which is used first to freeze tissue and then to thaw the tissue with a heating cycle. Nitrogen is supplied to a Joule-Thomson nozzle for the cooling cycle, and helium is supplied to the same Joule-Thomson nozzle for the warming cycle. Preheating of the helium is presented as an essential part of the invention, necessary to provide warming to a sufficiently high temperature. Essentially the same system, using helium gas to warm a cryosurgical probe, injected into the cryosurgical probe through the same supply line and Joule-Thomson nozzle used for cooling was clearly illustrated in 1986 by Soviet scientists E. N. Murinets-Markevich, et al. in Soviet Patent SU 1,217,377. Our own U.S. patent application Ser. No. 08/685,233 (filed Jul. 23, 1996), also uses Joule-Thomson warming in a system which provides for control of the freeze zone at the tip of the cryoprobe.
A Joule-Thomson cryostat for use as a gas tester is illustrated in Glinka, System for a Cooler and Gas Purity Tester, U.S. Pat. No. 5,388,415 (Feb. 14, 1995). Glinka also discloses use of a by-pass from the Joule-Thomson Nozzle to allow for cleaning the supply line, and also mentions that the high flow of gas in the by-pass mode will warm the probe. This is referred to as mass flow warming, because the warming effect is accomplished purely by conduction and convection of heat from the fluid mass flowing through the probe.
Various cryocoolers use mass flow warming, flushed backwards through the probe, to warm the probe after a cooling cycle. Lamb, Refrigerated Surgical Probe, U.S. Pat. No. 3,913,581 (Aug. 27, 1968) is one such probe, and includes a supply line for high pressure gas to a Joule-Thomson expansion nozzle and a second supply line for the same gas to be supplied without passing through a Joule-Thomson nozzle, thus warming the catheter with mass flow. Longsworth, Cryoprobe, U.S. Pat. No. 5,452,582 (Sep. 26, 1995) discloses a cryoprobe which uses the typical fin-tube helical coil heat exchanger in the high pressure gas supply line to the Joule-Thomson nozzle. The Longsworth cryoprobe has a second inlet in the probe for a warming fluid, and accomplishes warming with mass flow of gas supplied at about 100 psi. The heat exchanger, capillary tube and second inlet tube appear to be identical to the cryostats previously sold by Carleton Technologies, Inc. of Orchard Park, N.Y.
Still other Joule-Thomson cryocoolers use the mechanism of flow blocking to warm the cryocooler. In these systems, the high pressure flow of gas is stopped by blocking the cryoprobe outlet, leading to the equalization of pressure within the probe and eventual stoppage of the Joule-Thomson effect. Examples of these systems include Wallach, Cryosurgical Apparatus, U.S. Pat. No. 3,696,813 (Oct. 10,1973). These systems reportedly provide for very slow warming, taking 10-30 seconds to warm sufficiently to release frozen tissue attached to the cold probe. Thomas, et al., Cryosurgical Instrument, U.S. Pat. No. 4,063,560 (Dec. 20, 1977) provides an enhancement to flow blocking, in which the exhaust flow is not only blocked, but is reversed by pressurizing the exhaust line with high pressure cooling gas, leading to mass buildup and condensation within the probe.
Each of the above mentioned cryosurgical probes builds upon prior art which clearly establishes the use of Joule-Thomson cryocoolers, heat exchangers, thermocouples, and other elements of cryocoolers. Walker, Miniature Refrigerators for Cryogenic Sensor and Cold Electronics (1989) (Chapter 2) and Walker and Gingham, Low Capacity Cryogenic Refrigeration. pp. 67 et seq. (1994) show the basic construction of Joule-Thomson cryocoolers including all of these elements. The Giaque-Hampson heat exchanger, characterized by coiled finned-tube, transverse flow recuperative heat exchanger is typical of cryocoolers. The open mandrel around which the finned tube coil is placed is also typical of cryocoolers.
Each of the warming mechanisms of the prior art may be classified as mass flow warming (Glinka), reverse mass flow warming (Longsworth), Joule-Thomson warming (Murinets-Markevich, Ben Zion, and Mikus), or flow blocking (Wallach). In all of these systems, flow of cooling gas is supplied through a long high pressure line, usually several feet (one or two meters) of tubing to connect the cryoprobe with the gas supply manifold. When flow of cooling gas is cut off, there is a substantial volume of high pressure cooling gas in the supply line. This gas has only one place to go: through the cryoprobe, and Joule-Thomson nozzle, then out of the downstream exhaust line leading from the cryoprobe. It takes several seconds for the pressure to dissipate through the probe, and during this dissipation the Joule-Thomson effect continues and the probe continues cooling. This situation delays the desired warming of the cryoprobe and limits the control that a surgeon may exercise over the cooling and warming of tissue.
The cryosurgical system comprises a Joule-Thomson cryoprobe including a Joule-Thomson nozzle and a cryoprobe outlet. The Joule-Thomson nozzle is in fluid communication with the cryoprobe outlet. A high pressure gas supply line is aligned to supply gas to the Joule-Thomson cryoprobe. An operating cut-off valve is operatively connected to the high pressure gas supply line, the valve being operable to supply and cut off high pressure gas to the Joule-Thomson cryoprobe. A vent valve assembly is operatively connected to the high pressure gas supply line, the vent valve assembly being operable to vent gas from the high pressure supply line immediately upon operation of the operating cut-off valve to cut off high pressure gas to the Joule-Thomson cryoprobe. An interlock controls the vent valve assembly, the interlock being operable to open the vent valve assembly immediately upon operation of the cut-off valve to cut off high pressure gas to the Joule-Thomson cryoprobe. A backpressure source is operably connected to the cryoprobe outlet for supplying backpressure to the Joule-Thomson cryoprobe to minimize residual flow through the Joule-Thomson nozzle.